CM871 Engine cycle...

[KW660_16]

It depends on how the engine is used and what its HP ratings are. If you use more fuel with more engine pressures more piston ring seepage will occur and the oil will get contaminated sooner. I change my oil every 25K miles (thinking about shortening it) and I can tell diesel is in it and its thinner when I drain it. You really need to do oil analysis if you are going to extend oil changes so that you know EXACTLY what that oil is doing to your engine.